The early eighties saw a 30% drop in prices which basically unwound some of the large increases of the 70s that was due to the inflation seen in that decade. Prices then slowly increased from the reset baseline. The curve steepened around the millennium or soon after, then steepened again following the financial meltdown in 2007/8. QE has ensured that the supply of money is effectively unrestricted, with a lot of that finding its way into alternative investments for the collector, or easy credit for the spendthrift consumer. Should be a ready supply of used upper end motors in the not too distant future for anyone looking to pick and choose a restoration/old car collection hobby.